The present invention relates to anesthetic vaporizers. UK Patent No 1 224 478, describes an anesthetic vaporizer of the by-pass type in which a carrier gas such as oxygen, air or nitrous oxide is initially divided on entry to the vaporizer between a first stream which is directed towards the sump or vaporizing chamber of the vaporizer to entrain vapor from a volatile liquid anesthetic contained therein; and a second by-pass stream, the first and second streams subsequently recombining prior to leaving the vaporizer for delivery to a patient.
This known vaporizer has been used successfully over a number of years for delivering anesthetic agents such as halothane, trichloroethlne and halogenated ethers including enflurane, fluoroxene, methoxyflurane and isoflurane. All the aforementioned anesthetic agents have a boiling point at atmospheric pressure well above 40.degree. C.
However, a new anesthetic agent has been developed namely 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane which has a boiling point at atmospheric pressure of between 20.degree. and 25.degree. C. This physical characteristic of 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane renders existing anesthetic vaporizers unsuitable for delivering said agent to a patient.
Conventional vaporizers of the by-pass type are unsuitable for this new anesthetic agent in that its boiling point is approximately in the middle of their operating ambient temperature range, i.e. between 15.degree. C. and 35.degree. C. When the ambient temperature and hence the vaporizer temperature is above 25.degree. C., heat is transferred to the anesthetic agent which causes an amount of vapor to boil off such that heat lost by the latent heat of vaporization is equal to the heat transferred to it.
In conventional vaporizers the heat transfer to the anesthetic agent in the vaporizing chamber can be high because of the materials used and this can cause a high volume of anesthetic agent to boil off. This anesthetic vapor can leave the vaporizer via either the control valve, the by-pass valve or both.